Anticoagulation and ECMO:
Before Initiating Anticoagulation:
- A baseline set of coagulation studies should be obtained if possible before initiating systemic anticoagulation.
- These include a CBC (specifically platelet count), INR, aPTT, and fibrinogen.
- At TGH, rotational thromboelastography (ROTEM) can help elucidate coagulopathy and is useful in the postoperative setting.
- Any underlying coagulopathy should be corrected and investigated before initiating systemic anticoagulation on ECMO.
Initiation of Anticoagulation:
- When the baseline coagulation status has been established, systemic anticoagulation can begin.
- Intravenous unfractionated heparin (UFH) is what is used at TGH in most cases.
- Anticoagulation is guided by a nomogram, and the aPTT is checked routinely.
- Usually a bolus of 50-100 units per kg is given, and then an aPTT level is checked.
- There are two nomograms, a "medical" and "surgical" (see below).
- The difference is that the medical nomogram targets a slightly higher aPTT , because there is thought to be less concern for bleeding compared to a surgical patient.
Monitoring of Anticoagulation:
- Once anticoagulation is initiated, aPTT levels are checked on a routine interval.
- If there is fluctuation in the aPTT, the levels are measured more frequently.
- In a stable patient they may only need to be measured every shift or even once per day.
- Monitoring for bleeding is a fundamental part of ECMO patient care (see daily care of the ECMO patient for details).
- It is also important to monitor for clots in the circuit, which typically happen at the level of the oxygenator.
- Shining a flashlight on the filter before the oxygenator (called the pre-membrane filter) can reveal thrombosis.
- The filter after the oxygenator (called the post-membrane) filter should also be checked for clots, but they are less likely to form here.
- Sometimes the aPTT can be in the target range but there is evidence of ongoing clot formation, in this case the anticoagulation should be discussed with the team and potentially adjusted.
- If there is concern about haemorrhage, the surgical team should be informed immediately, and the heparin may need to be discontinued.
Heparin-Induced Thrombocytopenis (HIT) and ECMO:
- Patients on ECMO are at risk for developing HIT.
- Before sending the assay, make sure the "4Ts" screen warrants an immunoassay test.
- If the HIT assay is positive, hematology should be consulted.
- Plasmapheresis can be used to wash out the antibodies.
- Another non-heparin-based anticoagulant can be used.
- These two approaches are often used in consort.
Next page: Anticoagulation and ECMO: Non-heparin-based anticoagulation